It is often desirable to integrate RF antenna arrays into the outer surfaces (or “skins”) of aircraft, cars, boats or other vehicles, as well as in walls of commercial or residential structures (e.g., for use in wireless LAN applications). Ideally, such antennas are flush-mounted within the skins or walls. To accomplish this, it is desirable to use antennas or radiators having a low profile and a wide bandwidth frequency response.
Cavity-backed slot antennas or cavity-backed microstrip patch antennas are commonly used for airborne and satellite-based applications, because they can be flush mounted and are low cost and light weight. The cavity height is usually designed to be one-quarter wavelength or three-quarters of a wavelength of the resonator frequency to maintain impedance matching. The cavity height and, thus, volume can be reduced through dielectric loading, but the bandwidth and efficiency will also be reduced.
Surface waves produced in conventional cavity-backed patch radiators have undesirable effects. For example, scan blindness (e.g., loss of signal) can occur at angles in phased arrays where surface waves modify the array impedance such that little or no power is radiated at a particular scan angle. The array field-of-view is thus often limited by the angle at which scan blindness occurs due to surface waves. Further, currents are induced on a patch radiator due to the radiated space waves and surface waves from nearby patch radiators.